What voltage reading should be measured if the start pushbutton is pressed and the circuit is operating properly?

When the start pushbutton is pressed in an electric motor control circuit, it completes the circuit, allowing current to flow through the components involved in starting the motor. In a properly functioning system, this should result in the control circuit receiving the full control voltage.

The full control voltage is necessary to energize relay coils or contactors that facilitate the motor's operation. This voltage ensures that devices respond appropriately to start commands and maintain the necessary operational characteristics of the control circuit. Therefore, measuring full control voltage when the start pushbutton is pressed indicates that the circuit is correctly set up and functioning properly, allowing the motor to start as intended.

Other readings, such as no voltage or half control voltage, would indicate that either the circuit is not completed (open circuit) or there is a fault that prevents adequate voltage from reaching the control devices, which would hinder the operation of the motor. Similarly, motor voltage would measure the voltage across the motor terminals, which pertains to the motor's operational state but does not directly reflect the control circuit's status when the start button is engaged.